The physical behavior of polymethyl methacrylate-carbon dioxide (PMMA-CO₂) system was studied in a wide range of temperatures (0–100 °C) and pressures (0.1–10 MPa). The glass transition temperature of the systems was determined by a new optical observation methodology. The developed procedure is based on the refraction index variations between rubbery and glassy states, which allowed to differentiate both PMMA states for each pair of temperature and pressure conditions. Following this procedure, retrograde behavior was confirmed for three different grades of PMMA, finding significant differences in their behavior. In addition, the study of the glass transition temperature of the PMMA-CO₂ systems included the low-pressure and low-temperature region, scarcely studied before. The new results obtained in the low pressure-temperature region are critical to design advanced foaming approaches and manufacturing processes at low temperatures.

研究了聚甲基丙烯酸甲酯-二氧化碳（PMMA-CO ₂）系统在宽温度（0-100°C）和压力（0.1-10 MPa）下的物理行为。该系统的玻璃化转变温度是通过一种新的光学观察方法确定的。所开发的程序基于橡胶态和玻璃态之间的折射率变化，从而可以针对每对温度和压力条件区分两种PMMA状态。按照此程序，已确认三种不同等级的PMMA的逆行行为，发现它们的行为存在显着差异。另外，对PMMA-CO ₂的玻璃化转变温度的研究系统包括以前很少研究的低压和低温区域。在低压温度范围内获得的新结果对于设计先进的发泡方法和低温制造工艺至关重要。